<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <link rel="stylesheet" href="css/normalize.css" />
    <link rel="stylesheet" href="css/index.css" />
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  <body>
    <input type="text" class="input1" />
    <select class="select" >
      <option selected="selected">请选择</option>
      <option>+</option>
      <option>-</option>
      <option>*</option>
      <option>/</option>
    </select>
    <input type="text" class="input2" />
    <input type="button" value="=" class="button" />
    <input type="text" class="input3" value="" />
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  </body>
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